The long range goal of the proposed reseach is to understand the functional relationships of the secretory and systemic immune systems in fish. The general hypothesis to be tested is that the immunoglobulins (Igs) in secretions are chemically distinct and functionally independent from the Igs found systemically. The objectives proposed are four-fold. New evidence detailed in this proposal suggests that there is an unappreciated heterogeneity of the systemic Igs in fish which likely reflects differences inboth the heavy and light chain components. The first hypothesis to be tested is that this heterogeneity, which can be distinguished by presently derived monoclonal antibodies (Abs), is due to previously undetected isotype differences in the systemic Igs. Testing this hypothesis will involve both primary and secondary structural comparisons between the Ig subpopulations defined by the monoclonal Abs as well as population studies to determine whether these differences are allotypic or isotypic. The second hypothesis is that the Igs in secretions are chemically distinct from those found systemically and are regulated differentially in vivo. Testing this hypothesis will involve primary and secondary structural comparison of the secretory Igs to those found systemically. In addition, radioiodinated Igs from both the systemic and secretory systems will be injected intravenously to see if the Igs are regulated differentially. The third hypothesis is that there are lymphoid cells in anatomical juxtaposition to the secretory sites. This hypothesis will be tested by examining secretory tissues by immunofluorescense using monoclonal Abs to distinguish the site and the type of Ig produced by these cells. The last hypothesis to be tested is that the immunization route has a profound effect on the expression of Ab in the secretions as opposed to the systemic circulation. Defined antigens will be used in intragastric or intraintestinal vaccinations and will be compared to nonparenteral injections. The Ab produced will be quantitated and the type defined using the monoclonal reagents. These studies, therefore, should provide important basic information on the functional relationship of the secretory and systemic immune system in fish, provide a phylogenetic basis for Ig isotype divergence, and provide economically important information to a rapidly growing aquaculture industry.